Apparatus and method for implementing a suspend mode in an Ethernet-based communications system

ABSTRACT

The present invention describes a communications system having a first link partner and a second link partner that are connected by a communications link having at least four pairs of conductors. According to IEEE Standard 802.3 (e.g. Ethernet) for 1000Base-T, a data link is maintained (in a period absent data transmission) by sending idle signals over four pairs of conductors of the cable to maintain a logical connection. This idle signal scheme is replaced with an alternate idle signaling scheme that uses only two pairs of conductors to maintain a logical connection and therefore can operate with using lower power. The other two pairs of conductors of the four pairs of conductors are unused to maintain a logical connection absent data transfer, and therefore can be used to implement a Suspend Mode of operation. During Suspend Mode, the physical layer of each link partner powers down unnecessary circuitry so as to operate in a low power environment. To initiate the Suspend Mode, idle signals are sent on one of the un-used pairs of the conductors mentioned above. To exit Suspend mode, idle signals are sent on respective conductors simultaneously.

CROSS-REFERENCED TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/520,313, filed on Nov. 17, 2003, which is incorporated by referenceherein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to implementing a suspend modein an Ethernet-based communications system.

2. Background Art

High speed data links transmit data from one location to another overtransmission lines. IEEE Std 1394 (“Firewire”) includes a provision fora “Suspend” mode. Suspend mode allows the two ends of a link tosubstantially reduce their power consumption, while maintaining a lowlevel connection. In Suspend mode, neither end of a link can send data,but both ends remain aware of the other's presence. Therefore, anydisconnection of the link can be detected. The two ends of the link canmove from Suspend mode back to normal operation (passing data) morequickly than re-establishing a connection that has been fullydisconnected.

IEEE Std. 802.3 (“Ethernet”) contains no equivalent function. However,it would be desirable to have such a Suspend mode option in IEEE 802.3.

BRIEF SUMMARY OF THE PRESENT INVENTION

The present invention is directed to implementing a Suspend Mode in acommunications link, for example an Ethernet communications system. Thecommunications link includes a first link partner and a second linkpartner that are connected together by at least four pairs ofconductors, namely A, B, C, D. The communications link normally utilizesonly one of the conductor pairs (either A or B) for data transmission,and the other two pairs of conductors (C and D) are un-used for datatransmission. The link partners send idle signals on one of the pairs (Aor B), or both pairs A and B, to maintain an Active Mode for datatransmission. When there is no data to transmit, one of the linkpartners sends idle signals on an un-used pair (C or D) to initiate aSuspend Mode. The idle signals on the normally un-used pair oftransmission lines are recognized by both link partners to initiate theSuspend Mode, where one or more transmitters and receivers in each linkpartner are powered down in order to save power. The Suspend Mode ismaintained by continuing to send the idle signals on the normallyun-used pair of conductors (C or D). When one of the link partners isready to transmit data, then the Suspend Mode is terminated by sendingidle signals on one (or both) of the normally used pairs (A and B), andon one (or both) of the normally un-used pairs (C and D).

Further features and advantages of the present invention, as well as thestructure and operation of various embodiments of the present invention,are described in detail below with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described with reference to the accompanyingdrawings. In the drawings, like reference numbers indicate identical orfunctionally similar elements. Additionally, the left-most digit(s) of areference number identifies the drawing in which the reference numberfirst appears.

FIG. 1 illustrates a conventional communications link with four pairs ofconductors (A, B, C, D), including at least one pair of conductors (Cand D) that are not normally used for data transmission.

FIG. 2 illustrates a communications link with four conductors, whereconductors C and D are used to initiate Suspend Mode.

FIG. 3 illustrates a flowchart that describes initiation, maintenance,and exit of the Suspend Mode.

DETAILED DESCRIPTION OF THE INVENTION

“S800BaseT” is a high speed data link that uses a physical layer (PHY)from IEEE Std. 802.3 to carry 1394 Firewall data. S800T is furtherdescribed in U.S. patent application Ser. Nos. 10/748,290 and10/882,389, all of which are incorporated herein by reference.Furthermore, the 802.3 Ethernet standard and the IEEE Std 1394 areincorporated by reference herein in their entirety.

As discussed above, the Suspend mode in IEEE 1394 allows the two ends ofa link to substantially reduce their power consumption, whilemaintaining a low level connection. In Suspend mode, neither end of alink can send data, but both ends remain aware of the other's presence.There is no 1000BASE-T equivalent to “Suspend” mode in IEEE Std 802.3.However, as discussed above, this would be desirable. Even know theinvention is described in terms of IEEE Std. 802.3, the invention is notlimited to this application, and could be used for other applications aswill be understood by those skilled in the arts.

FIG. 1 illustrates a conventional S800Base-T communications systemhaving four pairs of conductors 104, namely, pair A, pair B, pair C, andpair D. As shown, the 4 conductor pairs 104 connect a first link partner102 to a second link partner 106. For Ethernet, the conductors could betwisted pair, but the invention is not limited to twisted pair, andcould use other transmission line connections between the first andsecond link partners.

When a physical layer “LINK” is established in conventional S800Base-T,opposite ends are synchronized in a master/slave relationship. This isuseful for proper cancellation of Near End Crosstalk (NEXT) and Far EndCrosstalk (FEXT). Link start-up is based on values derived fromauto-negotiation Next Pages. Link start-up time can be significant, as1000BASE-T devices are allowed 750 ms after completion ofauto-negotiation to establish a link.

According to IEEE Standard 802.3 (e.g. Ethernet), an Active Mode fordata transmission is maintained by sending idle symbols when there isactually no data to transmit. In other words, a logical connection ismaintained between link partners by the idle signals absent actual datatransmission. In 802.3 10BASE-T, these idle symbols consist of normallink pulses (“NLPs”) on a first pair or a second pair of conductors ofthe communications link. For example, the idle signals are sent onconductor pairs A or B of the four pair of conductors that are shown inFIG. 1. In 802.3 100BASE-TX, these idle symbol are higher speed MLT-3idle code, also on a first pair or a second pair of conductors of thecommunications link. In 802.3 1000BASE-T, these idle symbols are higherspeed PAM5 idle code, which is sent simultaneously on all four pairs at125 MHz on each line. The IDLE pattern for 1000BASE-T consumes as muchtransmit power as data. Cessation of the IDLE pattern results in linkdrop, followed by restart of auto-negotiation. It can take severalseconds to re-establish the link after a link drop.

The present invention includes a modified form of IEEE Std. 802.3 thatenables a Suspend Mode to be implemented in 1000Base-T. In oneembodiment of the invention, 1000Base-T is modified so that idle signalsare transmitted only on the first and/or second pairs of the conductors104, instead of all four pairs. This enables the other two pairs ofconductors to be used for signal transitions and maintenance of aSuspend mode in IEEE 802.3 1000Base-T on the un-used conductor pairs.

For example, FIG. 2 illustrates that idle signals for IEEE Std.1000Base-T are transmitted on conductors 1 and 2 (pair A), and/or onconductors 3 and 6 (pair B) to maintain a logical connection in ActiveMode, absent any actual data transmission. The other two pairs ofconductors (C and D) do not carry idle signals in Active Mode, andtherefore are unused. Therefore, in one embodiment of the presentinvention, idle signals that are sent on the un-used conductor pairs C(conductors 4 and 5) and/or D (conductors 7 and 8) are interpreted to besignal transitions (including initiation) and maintenance of the SuspendMode. Since the alternate pairs C and D are not examined in conventional1000Base-T (or S800Base-T), such transitions and maintenance of theSuspend mode signals do not appear in any legacy 802.3 application.

Some unique signals are used to initiate a Suspend mode in order totransition from Active mode to Suspend mode. Furthermore, some uniquesignals are required to maintain the Suspend mode. Disconnection of thelink is identified by the absence of the signal that causes theconnection to be dropped. After a disconnection is detected, then thelink can be restarted. The transition from Suspend mode back to Activemode also uses some unique signals to exit Suspend mode and get back tothe Active state. In one embodiment, this requires some clocksynchronization, but should not re-start Auto-negotiation. That is,suspend mode is not full disconnection. The signals for Suspend modeinitiation and link re-activation are discussed further below inrelation to FIG. 3.

The initiation of the transition from Active mode to Suspend mode willnow be discussed in reference to the flowchart 300 that is shown in FIG.3. In step 302, auto-negotiation occurs between the PHYs of the linkpartners (e.g. link partners 102 and 106) to start data transfer. Instep 304, normal data operation occurs to send data and idle signalsbetween the link partners 102 and 106. In step 306, either link partnernotices the absence of data traffic between the link partners for aspecified time period, thus initiating the Suspend Mode. In step 308,one of the link partners instructs the local PHY to enter Suspend Modebased the on absence of data traffic. During initiation in step 310, thelocal PHY in the first link partner sends an idle signal pattern onconductor pairs C and/or D to the second link partner to initiate theSuspend Mode. These idle signals on pairs C and/or D are interpreted asSuspend Mode signals, since these pairs C and D are normally un-used forActive Mode idle signals in the modified version of IEEE 802.31000Base-T discussed above. Accordingly, the second link partnerrecognizes idle signals on pairs C and/or D as initiating Suspend Modeand responds with a similar transmission of idle signals on pairs Cand/or D, so that both link partners enter the Suspend Mode.

During Suspend Mode, both PHYs in their corresponding link partnerscontinue transmitting idle signals on the pairs C and/or D in step 312so as to maintain the Suspend Mode. In step 314, each PHY powers downunneeded circuitry so that one or more transmitters and receivers arepowered off. For example, three of the four transmitters and receiverscan be powered off almost completely. For instance, the NEXT/FEXTcancellers, adaptive filters, and Analog-to-Digital Converters (ADCs)are powered off. Pads and signal detect functions remain powered up. Bydoing so, power is reduced by >80%, to <100 mW (although these resultsare implementation specific).

The Suspend mode enables detection of a physical disconnect between thefirst link partner and the second link partner. For instance, theSuspend mode enables detection when the cable is pulled out of theconnector, or when a link partner loses power. If the cable isdisconnected, or either link partner ceases functioning, then the idlesignals on pairs C or D will cease. A PHY that no longer receives idlesignals will disconnect and re-start the Auto-negotiation. Disconnectioncan be forced through software commands at either link partner, if it isdesired to restart Auto-negotiation.

If either end of the link requires data to be sent, it can initiate anexit from the Suspend Mode, which is referred to as Resume Mode. In step318, the local node signals the local PHY to enter Resume mode. In step320 in Resume Mode, the PHY at either link partner sends idle signals onpairs C and/or D and simultaneously sends idle signals on pairs A and/orB. In step 322, the other end of the link receives the idle signals onall four conductor pairs simultaneously and recognizes this as aninstruction to exit Suspend Mode. All parameters from the previousauto-negotiation state in step 302 are preserved. Both ends synchronizeclocks, send PAM5 IDLE signals, and begin data transmission to re-enternormal operation in step 304. In one embodiment, this is identical tothe steps following successful Auto-negotiation, where auto-negotiationis a start-up procedure.

Some of the advantages of the Suspend Mode are as follows. Entering andexiting Suspend mode enables low power operation when data is not beingtransmitted. Furthermore, the Suspend Mode keeps the physical connectionactive by sending the idle signals, and allows cable disconnects to bedetected. The Suspend Mode leverages existing signaling levels andtiming of idle signals. For instance, this allows 1000BASE-T PHYarchitecture to be used with only small modifications. This uses analternate pair for idle signaling the Suspend mode, to prevent anyconfusion with idle signals sent during Active mode. Further, theSuspend Mode uses pairs C and D of a four pair conductor set, which arenormally “unused” for all 802.3 Auto-negotiation and Link PulseSignaling.

Although the invention is described in terms of IEEE Std. 802.3, theinvention is not limited to this application, and could be used forother applications as will be understood by those skilled in the arts.Further, the invention is not limited to a communications link with fourpairs of conductors. Instead, any number of conductors could be used, aslong as one or more pairs of conductors are normally un-used for datatransmission. Further, the invention is not limited to use with twistedpairs, but could be used with any type of transmission line.

CONCLUSION

Example embodiments of the methods, systems, and components of thepresent invention have been described herein. As noted elsewhere, theseexample embodiments have been described for illustrative purposes only,and are not limiting. Other embodiments are possible and are covered bythe invention. Such other embodiments will be apparent to personsskilled in the relevant art(s) based on the teachings contained herein.Thus, the breadth and scope of the present invention should not belimited by any of the above-described exemplary embodiments, but shouldbe defined only in accordance with the following claims and theirequivalents.

1. A communications system, comprising: a first link partner; a secondlink partner; and a communications link between said first link partnerand said second link partner that includes at least four pairs ofconductors; wherein idle signals are sent on first and second pairs ofconductors of said at least four pairs of conductors to maintain alogical connection in an Active Mode of said communications link;wherein idle signals are sent on third or fourth pairs of conductors ofsaid at least four pairs of conductors to initiate a Suspend Mode ofsaid communications link; and wherein said Suspend Mode is ended bysending idle signals on said first and second pairs of conductors, andsimultaneously sending idle signals on said third and fourth pairs ofconductors, as recognized by said first and second link partners.
 2. Thecommunications system of claim 1, wherein a physical layer in each ofsaid first link partner and said second link partner powers-downcircuitry during said Suspend Mode.
 3. The communication link of claim2, wherein said physical layer powers down a portion of a transmitter ora receiver in each of said first link partner and said second linkpartner during said Suspend Mode.
 4. The communications link of claim 3,wherein at least one of a NEXT/FEXT canceller, an adaptive filter, andan Analog-to-Digital Converter (ADC) is powered down.
 5. Thecommunications link of claim 2, wherein said physical layer in each linkpartner includes one or more transmitters and one or more receivers,said physical layer in each link partner powering off all but onetransmitter and one receiver.
 6. The communications system of claim 1,wherein said communications link operates so that said third and fourthpairs of conductors are normally un-used during data transmission. 7.The communications system of claim 1, wherein said communications linkis operating according to an IEEE 802.3 protocol.
 8. The communicationssystem of claim 1, wherein said communication link uses physical layersfrom IEEE Standard 802.3 to transmit data associated with an alternativeprotocol.
 9. The communications system of claim 8, wherein saidalternative protocol is IEEE Standard
 1394. 10. In a communicationssystem having multiple transmission lines connecting first and secondlink partners, at least one transmission line un-used for datatransmission, a method of operating a Suspend Mode when no data trafficis flowing between said first and second link partners over saidmultiple transmission lines, the method comprising: sending idle signalson a first transmission line of said multiple transmission lines tomaintain a logical link on said first transmission line; detecting anabsence of data transfer between said first link partner and said secondlink partner on said first transmission line; sending idle signals on asecond transmission line of said multiple transmission lines to initiatea Suspend Mode between said first link partner and said second linkpartner based on said absence of data transfer on said firsttransmission line, said second transmission line is un-used for datatransfer; and resuming data transmission between said first link partnerand said second link partner, including sending idle signals on bothsaid first transmission line and said second transmission line toinitiate a Resume Mode for data transfer; and resuming data transferbetween said first link partner and said second link partner based onsaid Resume Mode.
 11. The method of claim 10, further comprising thestep of: powering down a portion of a transmitter and a receiver in eachof said first link partner and said second link partner during saidSuspend Mode.
 12. The method of claim 11, wherein said first linkpartner and said second link partner each have a plurality oftransmitters and receivers, further comprising the step of: at each linkpartner, powering down all but one transmitter and one receiver duringsaid Suspend Mode.
 13. The method of claim 11, further comprising thestep of maintaining said Suspend Mode by continuing to send said idlesignals between said first link partner and said second link partnerover said second transmission line.
 14. The method of claim 10, whereinsaid communications system operates according to IEEE Standard 802.3.15. The method of claim 10, wherein said communication link usesphysical layers from IEEE Standard 802.3 to transmit data associatedwith an alternative protocol.
 16. The method of claim 15, wherein saidalternative protocol is IEEE Standard
 1394. 17. In a communicationssystem having four pairs of conductors connecting first and second linkpartners, first and second pairs of said conductors used for datatransmission and third and fourth pairs of said conductors un-used fordata transmission, a method of operating a Suspend Mode when no datatraffic is flowing between said first and second link partners over saidfirst and second pairs of conductors, the method comprising: during anActive Mode, sending idle signals on either of said first and secondpairs of conductors to maintain a logical connection; detecting anabsence of data on said first and second pairs of conductors for aminimum time interval; sending idle signals on either one of said thirdand fourth pairs of conductors to initiate a Suspend Mode between saidfirst link partner and said second link partner based on said absence ofdata on said first and second pairs of conductors; and if there is datato transmit between said first link partner and said second linkpartner, then sending idle signals on one of either said first andsecond pairs of conductors and sending idle signals on one of eithersaid third and fourth pairs of conductors; and resuming data transferupon receiving said idle signals on one of either said first and secondpairs of conductors and upon receiving said idle signals on one ofeither said third and fourth pairs of conductors.
 18. The method ofclaim 17, further comprising the steps of: powering down all but onetransmitter and one receiver in each of said link partners during saidSuspend Mode; sending idle signals over either said third or fourthpairs of conductors to initiate said Suspend Mode using said onetransmitter and said one receiver in each link partner that is notpowered down.